>>7053162One of the slowest projectiles fired from the Challenger 2 is actuall still over 2 times the speed of sound. A typical combat round can be as fast as MACH 4.
The M1A1 Abrams' and Leopard's Rheinmetall gun can shoot cartridges with a velocity exceeding MACH 5, the Challenger's gun can reach that as well with very specific ammunition.